1. Field of the Invention
The present invention relates to an image processing apparatus for creating an image file which stores image data and parameters to specify processes for the image data, and a method of controlling the same.
2. Description of the Related Art
In recent years, digitization of information is encouraging the use of digital images in various fields. Various kinds of additional information such as a creation date and time and parameters for image processing can be added to a digital image (a data set including the image data of a digital image and its additional information will be referred to as an “image file” hereinafter). On the other hand, problems concerning security of digital images have received a great deal of attention. A digital image has an advantage of being readily edited. However, this also means that alteration is easy. Data alteration is mainly made by malicious users. While there is assumed data alteration targeted at specific data, the target data for data alteration are not always predictable. For this reason, data alteration is considered an unknown threat.
If an image file is altered, its reliability cannot be guaranteed. For example, assume that an image file of high confidentiality stored in an image forming apparatus is altered in some way. In this case, if the user prints the image file or sends it to another PC or server without being aware of the alteration, incorrect information is circulated, potentially causing great danger. Hence, demand has arisen for a technique of detecting the alteration of an image file and performing appropriate control in accordance with the detection result.
Japanese Patent Laid-Open No. 2007-180873 discloses a technique of, when generating an image file, calculating a hash of image data included in the image file and additional information such as image capture parameters, operating the hash using a private key, and adding resultant information to part of the image file. When printing the image file, a hash is calculated in accordance with the same procedure as in generating the image file, and compared with the hash value added to the image file. If the values do not coincide, alteration is detected. If alteration is detected, control is performed to prohibit printing of the image file or to notify the user of the alteration and require him/her to determine whether or not to print the image file.
However, the method of Japanese Patent Laid-Open No. 2007-180873 is merely to control to, upon detecting alteration of an image file, prohibit printing of the image file or comply with the user's instruction. There is a problem of security because even a highly confidential document that should not be printed can be printed in accordance with a user's print instruction. Conversely, when printing is completely prohibited upon detecting alteration of an image file even if the altered portion poses no problem at all in printing, user convenience may be negatively affected.